Currently, an elementary magnetic storage cell on a medium in the form of a disk or tape requires a superficial area of about 100 to 120 square micrometers. One cell is described by the width of the recording track (usually 20 micrometers) and by the number of bits per unit of length.
Elementary cells with, a superficial area of 0.5 to 25 square micrometers and a surface density almost equal to 1 bit per square micrometer are currently envisaged. The reading and writing of information on such cells necessitates new type of magnetic heads offering improved performances.
According to the prior Art, three different types of heads currently exist : the first type is the normal type relating to monolithic or solid-state heads, the second is formed by heads made up of thin layers and the third corresponds to hybrid or composite heads.
Owing to the magnetic volume involved, mono and mini-monolithic heads generate significant noise and possess poor resolution. Their method of production limits access to large densities and renders difficult passage to densities greater than 1200 TPI (tracks per inch).
Heads consisting of thin layers have many advantages, but they are costly and complex to produce and volume production remains quite small.
Only hybrid or composite heads allow access to large recording densities while keeping production costs relatively low. Their current performances fall between those of the other types of heads.